Fabricating hierarchical, multi-material structures offers tremendous promise for controlling and tailoring material properties. An example that highlights both the potential and the challenges of hierarchical, multi-material structures is discussed in “Simultaneously High Stiffness and Damping in Nanoengineered Microtruss Composites,” ACS Nano, Mar. 12, 2014, pp. 3468-3475. The microtruss composite possesses the contradictory design goals of high stiffness and high damping. These structures have sound absorbing qualities in cars and airplanes while also being strong. Fabrication of these structures involves the growing of carbon nanotubes (CNTs) from a steel plate and coating with alumina using traditional semiconductor processes, followed by multiple deposition steps to build a polyurethane/clay layer on the CNTs and finally encapsulation with polyurethane. This material is graded with the interface between the polymer and CNT microtruss composed of a nano-composite polymer that has intermediate properties, which is important for overall mechanical robustness. However, this method is not scalable to large areas or digital.
US Patent Publication 2011/0079936, to Oxman, explores concepts on digitally printing graded materials using dye in a FDM (fused deposition modeling) print head. The disclosure teaches ‘on the fly’ blending of materials for creating continuous gradients in material properties. However, this concept does not have the capability to build multiscale structures or heterogeneous material structures required to achieve the full potential of architected materials.